1. Field of the Invention
This invention relates to display systems capable of simultaneously displaying a frame of text and control codes.
2. Description of Prior Art
Office machines for processing text data to produce hard copies utilize display screens for visually displaying text to an operator as the text is originally keyed or later edited. Typically, such machines incorporate a conventional typewriter keyboard with additional control keys for operator interface with the system controls. The operator keystrokes are often displayed on a cathode ray tube (CRT) screen quite similar to a home television receiver screen. This screen may display a full page of text, a partial page, or in some machines only a single line of text. The display may provide, in addition to a visual presentation to the operator of the text being prepared, prompting instructions for the operator of how to interface with and operate the machine.
Responding to the keyboard strokes of an operator are system controls including programmed computers which prepare the text display. Most present day text processing systems include electronics hardware programmed to recognize the operator keystrokes and to control the display. This hardware includes memory for storing character data and instruction data for future use in editing and in the preparation of hard copy. Ease of operation of the machine by the operator is in large part determined by the electronics and the associated computers and programs therefor.
An area of importance in determining the ease with which an operator interfaces with a machine is the movement of a cursor, that is, an identification mark on the screen indicating a character position. A cursor has been typically used by an operator in text editing functions including the insertion of additional characters into text, identifying characters or blocks of characters to be moved, deleted or copied, and the reformatting of the text display.
An escapement scale line as a part of the display frame has also been employed in prior art systems to provide another operator aid. The scale line on the display screen is used in the same way by the operator creating and editing the text as is the familiar scale line on the typewriter as an aid to the operator in determining the relative horizontal position along the line at which an editing operation is to occur in accordance with the then present cursor position.
The cursor, heretofore referred to will hereafter be referred to as the text cursor. Another cursor has sometimes been included adjacent the scale line and has been called the ghost cursor. This cursor reflects the horizontal line position of the text cursor by highlighting this horizontal position adjacent the scale line so that it is unnecessary for the operator to note the horizontal position of the text cursor and then look vertically up the screen to determine the exact horizontal position of the text cursor in accordance with the scale line markings.
As an additional operator aid, prior art text display systems have been operable in two different modes of operation for displaying text. In the normal or hidden codes mode, control codes such as required backspace, carrier return, tab, etc. codes are not visually displayed to the operator unless the text cursor is presently addressing such a code in memory in which case only that single code is displayed as a control code. What has been displayed to the operator in the hidden codes mode (ignoring the scale line, code at the cursored location, or any prompting lines) is the text as it will be actually printed on a page of paper. Thus, alphanumeric characters and symbols are displayed including such characters as underscore characters since this kind of text is printed. On the other hand, if the word cat is keyed as "c", "a", "t", "required backspace", "required backspace", "required backspace", " ", " ", " ", this appears on the printed page as "cat". If the operator keys this text as just described and decides to remove all of the underscoring except the underscore under the first letter, "c", of the word, one way to do this would be to remove the second two underscore characters and add two space codes in their place. Another was to do this would be to remove all of the required backspace codes and all of the underscore codes from their original positions and add a single required backspace code and a single underscore code after the "c", and before the "a", in "cat". In either of these cases it is a great benefit to the operator to display all of these codes in a serial fashion, including the non-printing required backspace codes in the second of the two prior art display modes known as the all codes mode. In this mode the operator positions the text cursor adjacent the appropriate backspace or underscore codes to be deleted or otherwise edited and is able to easily access these normally non-displaying codes when they are, in this mode, displayed.
In the all codes mode however, due to the operation of linearly and sequentially displaying all of the codes in a serial fashion relative to each line of text, it becomes very difficult to visualize a given cursored position relative to where the cursor would actually be in the normal or hidden codes mode and, therefore, where the operating point would actually be on a printed page of text. The problem is perhaps most easily understood when considering the editing of a multi-columnar document in which a relatively large number of normally non-displaying control codes are included with the entries in each column. When editing such a document in the all codes mode it is quite possible to observe the text cursor position significantly beyond the outer boundaries of the particular column in which the text associated with the text cursor position is to be displayed. In extreme cases an operator might observe the text cursor in a horizontal frame segment separate from the frame in which the column of text is normally shown in the hidden codes mode.
It would, therefore, be of great advantage and utility for an operator to be provided with an indicator to show, while operating in the all codes mode, the horizontal position at which the text cursor would be located if the display were presently operating, instead, in the hidden codes mode.